Asthma and other respiratory diseases have been treated by the inhalation of appropriate medicaments. For many years the two most widely used and convenient choices of treatment have been the inhalation of medicament from a drug solution or suspension in a pressurized metered dose inhaler (pMDI), or inhalation of powdered drug, generally admixed with an excipient, from a dry powder inhaler (DPI). Following concern about a link between depletion of the earth's ozone layer and chlorofluorocarbon (CFC) emissions, interest in DPI systems has increased.
Most DPIs use either bulk powder reservoirs or individual pre-measured doses. In general, DPIs include an air passage leading from a dispensing chamber and terminating in a port for inserting into the users mouth or nasal passage. Inhalation at the port brings air through the dispensing chamber, carrying particles of medicament into the lungs of the user. Development efforts in this area have focused primarily on problems associated with accurately metering a measured small quantity (e.g. 500 micrograms or less) of powder either from a bulk reservoir within an inhaler or from a capsule or blister. In some instances such as with potent drugs, excipients such as lactose powder have been added, increasing the quantity of powder for accurate metering or for other reasons to up to, for example, at least 1 milligram. Such excipients may be undesirable as they can pose subsequent powder agglomeration or deagglomeration problems and can cause dryness and other unwanted effects in the patient's mouth. Traditional DPIs require carrier excipients, such as lactose, which dilute out the effective dose and increase the total mass of formulation needed.
One example of dry powder inhalers includes those in which predetermined doses of medicament are dispensed from a sheet material including discrete microdepressions (having a depth of about 5 to 500 microns and an opening at the surface of the sheet material of about 10 to 500 microns in width) filled with medicament. DPIs of this nature are disclosed in U.S. Pat. Nos. 5,408,994, 5,437,271, 5,469,843, 5,482,032, and 5,655,523.
However, there continues to be an interest and need for improved DPIs, which provide, for example, greater patient comfort and effectiveness and/or improved dosing capability.